1. Field of the Invention
The present invention relates to a radio wave correction clock which corrects time based on a time calibration signal (standard time and frequency signal) containing a time code.
2. Description of the Related Art
Currently, time calibration signals containing time codes are transmitted from a radio station. As a time calibration signal, time information such as year (the last two digits of a dominical year), hour, minute, etc. is serially transmitted as a binary code in the unit of one frame per minute. Specifically, one bit is represented as a rectangular pulse of 1 Hz, and “1” and “0” are represented by different pulse widths. And each time information piece is represented as a binary code. In some cases, a marker (frame reference) for identifying the start of one-frame data and a marker (frame reference) for identifying the start of each data (block) within a frame are used. In such cases, the markers are represented by pulse widths different from the pulse widths used in the above-described binary code.
A clock which corrects time by receiving a time calibration signal supplies power to its reception circuit for a predetermined time period from a predetermined time, receives a time calibration signal containing time information, and corrects time if it can receive it accurately.
However, such a clock may not be able to fully receive the time information, if the clock is installed in a place where a time calibration signal is hard to receive, or if there are influences of noise.
As a solution to this problem, Unexamined Japanese Patent Application KOKAI Publication No. H11-304973 (Reference 1) discloses a radio wave correction clock which determines received data containing time information such as year, month, day, and time (hour and minute) for each block in order to determine a block which has been received successfully, and continuously receives only a block which has not been received successfully.
Further, Unexamined Japanese Patent Application KOKAI Publication No. 2002-82186 (Reference 2) discloses a radio wave clock which receives block data of year, month, day, and time (hour and minute) during one unit period including a plurality of cycles, sequentially stores blocks which have been successfully received, and regards time information whose blocks have been all successfully received as provisional time information. This radio wave clock performs this process for two unit periods to obtain two pieces of provisional time information, and determines whether time is correct or not by comparing the two pieces of provisional time information.
Furthermore, Unexamined Japanese Patent Application KOKAI Publication No. 2002-131456 (Reference 3) discloses a radio wave clock which stores normal blocks other than error blocks if there are any such error blocks in part of the time information such as hour, minute, etc., and then advances its internal clock. If data obtained at the next reception time coincides with the data of the advanced time, this radio wave clock corrects time based on the received time data.
According to the invention of Reference 1, the block data of year, month, day, and time (hour and minute) which pass the parity check are determined as correct time information. However, since the block data which is first determined as correct is not necessarily correct, time correction might be performed based on an incorrect time.
According to the invention of Reference 2, block data which passes binary detection (detection of whether a bit is “0” or “1”) is regarded as correct time information and stored, and is not overwritten in the corresponding one unit period. However, since the block data that is stored first is not necessarily correct, time correction might be performed based on an incorrect time.
According to the invention of Reference 3, block data of year, month, day, and time (hour and minute) in the received data which pass the parity check are regarded as correction time information. However, in a case where either of time information contained in data received first and time information contained in data received next is incorrect, the two times compared with each other do not coincide. Therefore, time correction is not performed.